diff --git a/lua/json/decode.lua b/lua/json/decode.lua
index da01c01..c9dd457 100644
--- a/lua/json/decode.lua
+++ b/lua/json/decode.lua
@@ -104,9 +104,6 @@ local function generateDecoder(lexer, options)
 	local function diagnostic_decoder(data)
 		local state = decode_state.create(options)
 		local parsed = diagnostic_parser:match(data)
-		if not parsed then
-			error("Invalid JSON data")
-		end
 		local last_pos = 1
 		local i = 0
 		local ok, err = pcall(function()
@@ -133,7 +130,8 @@ local function generateDecoder(lexer, options)
 			local line, col, char, last_line = util.get_invalid_character_info(data, last_pos)
 			error(err .. (" @ character: %i %i:%i [%s] line:\n%s"):format(last_pos, line, col, char, last_line))
 		end
-		return state.previous
+		-- This line should never be reached since diagnostic_decoder is only run on failure paths
+		assert(false, "Diagnostic decoder finished without throwing an error")
 	end
 
 	local decoder = function(data)
diff --git a/tests/lunit-error-reporting.lua b/tests/lunit-error-reporting.lua
index a03c9a7..d3a0af7 100644
--- a/tests/lunit-error-reporting.lua
+++ b/tests/lunit-error-reporting.lua
@@ -126,3 +126,25 @@ end
 function test_missing_array_value()
 	assert_decode_error('[1,, 2]', "Expected value in array", nil, 1, 4)
 end
+
+-- Test: expected utility helper with multiple arguments
+function test_util_expected_helper()
+	local util = require("json.decode.util")
+	local pattern = util.expected("foo", "bar")
+	local ok, err = pcall(function()
+		pattern:match("data")
+	end)
+	assert_false(ok)
+	assert_not_nil(string_find(tostring(err), "expected one of 'foo','bar'", 1, true))
+end
+
+-- Test: expected utility helper with single argument
+function test_util_expected_single_helper()
+	local util = require("json.decode.util")
+	local pattern = util.expected("baz")
+	local ok, err = pcall(function()
+		pattern:match("data")
+	end)
+	assert_false(ok)
+	assert_not_nil(string_find(tostring(err), "expected 'baz'", 1, true))
+end